Deans Garage has posted a treasure trove of GM design studies from the 1960s through the 2000s, grouped by designer:

David McIntosh: http://www.deansgarage.com/2015/davi...h-gm-designer/
Includes
*Early variants on Cadillac Art-and-Science theme. Including a very small (front-drive?) model and a very large one (DeVille/Fleetwood replacement?).
*All sorts of wacky early efforts at what became the Lambda models.
*A Lumina replacement that might have given the Chrysler LH a run for its money.
*A 4WD Lumina APV.
*And much, much more....

I love looking at these designs, evolution's, themes, eventual executions - but also seeing hints of design in other areas / products. The Caddy 'SUV' that seems to be based upon the Hummer looked interesting.